Functional polymers with potentially useful optical and electronic properties have received significant attention due to the ability of these materials to improve upon existing technologies by combining the unique properties of small functional molecules (e.g., electron transfer, light absorption/emission, magnetic) with the processability, mechanical robustness, and flexibility associated with polymers. An interesting subclass of functional polymers that has emerged in recent years contain stable organic radicals1 in the repeating unit pendant to their backbones.2-4 The vast majority of research towards stable radical polymers has been motivated by their utility as electrode materials in batteries, where the introduction of conductive (nano)fillers has led to enhanced performance. However, radical polymers have also shown application as high-spin ground state materials, (co)catalysts for the selective oxidation of alcohols, inhibitors of self-polymerization reactions, solid-state conductive materials,5-7 and the functional component of memory architectures.8-10 
The most widely studied family of stable radical polymers is based on 2,2,6,6-tetramethyl-piperidin-1-yl (TEMPO, 1) radicals,11-19 while examples based on other families of radicals, including nitronyl nitroxide (2),20 2,2,5,5-tetramethyl-1-pyrrolidinylloxy (PROXYL, 3),21 spirobisnitroxide (4),22 aminoxy (5),23 galvinoxyl (6),24 and 6-oxoverdazyl (7)25 radicals have received considerably less attention (FIG. 1). Further expansion of the stable radical polymer field to include examples based on these and other stable radicals will allow for the realization of materials with targeted properties that are suitable for the applications described above. 6-Oxoverdazyl radicals offer exceptional stability towards air and moisture, and, while their high molecular weights render them poor candidates for battery applications, their tunable ambipolar redox properties may allow for their future use as charge transport materials.
Most synthetic protocols, for example those targeting nitroxide radical polymers, involve the polymerization of monomers based on radical precursors followed by post-polymerization reactions designed to generate the targeted stable radical polymers. These strategies are often hampered by difficulty surrounding the complete conversion of the radical precursor repeating units to their stable radical form, a factor that has recently been shown to affect their charge transport properties. Therefore, there remains a need for further development of polymerization protocols that allow for direct polymerization of stable radical-containing monomers and ensure a high degree of radical content along the polymer backbone.
Memory devices are a critical component in the field of information technology. They can be divided into volatile and nonvolatile, depending on the time for which they can retain the stored information. Volatile memory devices, including dynamic and static random access memory components, require stored data to be refreshed every few milliseconds. They cannot store data after the removal of the voltage used to write them. Most electronic systems require nonvolatile memory components for bootstrap and persistent data storage. To date, the most common nonvolatile memory components used in information and communication technology are devices that are writable once and readable multiple times (WORM). Flash memories that are writable, readable and erasable multiple times are more attractive, because they can be reused, but their costs are still high. Silicon-based flash devices consisting of a metal-oxide-semiconductor field effect transistor, with high k-dielectric oxides and an additional floating gate in each memory pixel, have been dominating the market of non-volatile devices writable and erasable multiple times, but suffer from limited margins of improvement and high fabrication costs. Inorganic floating gates used to store the information cannot be less than 32 nm thick in such components.
Organic memristors, memory devices based on organic thin films with multistable resistivity characteristics, are being explored as possible substitutes for volatile, WORM and flash inorganic memory devices. They have the advantage of low fabrication costs and can be processed from organic compounds in solution. Although continuous organic thin films with thicknesses down to 10 nm have been demonstrated,26 the minimum thickness that can be reached by organic “flash” memristors is still too high, at more than 15 nm. Proposed systems for organic memory devices include polyimide containing moieties, polymers containing metal complexes and non-conjugated polymers incorporating other organic materials (e.g., fullerenes, graphene oxide, carbazoles) directly and blended with polymers.
In most of these devices, two or more layers or phases are required, which poses insurmountable limitations to the ultimate thinness of the device. Flash memory devices comprising only a single layer of polymer are essential to keep their thickness to a minimum, and have been proposed. Another significant issue with organic memristors is to obtain stable flash effects, devices that are reproducibly writable a very large number of times. For instance, although memory devices based on radical polymers have been proposed,8,17 their stability so far has been limited to a few writing cycles, in spite of the excellent quality of the active layer, which indicates that more fundamental knowledge of the physics of these devices is required.